Electric vehicles are known in the art. They include one or more battery that supplies energy to one or more electric motors that in turn provide motive force to the vehicle. Each battery is generally charged overnight for use during the day. In these vehicles each battery can undergo regular deep cycling of its state of charge and thus each battery life expectancy is typically short. It is undesirable to discharge a battery too far as this also shortens battery life.
Hybrid electric vehicles are known. One type of hybrid vehicle includes an auxiliary power unit that can be used to generate energy during use of the vehicle. This energy can be used to supplement battery energy or to charge the battery. With the availability of an auxiliary power unit within the vehicle it is desirable to have a battery management system which regulates battery and auxiliary power unit operation and avoids overcharging of the batteries, which can reduce battery life.
A number of battery management systems are known, however they generally only perform any real control during overnight charging. During use the auxiliary power unit is often run continuously at a predetermined and fixed power output. This can result in overcharging of the battery. Alternative schemes only run the auxiliary power unit if the battery voltage, or state of charge, falls below a predetermined level. This does not overcome problems with state of charge cycling.
In the publication “Distributed VRLA Battery Management Organisation with Provision for Embedded Internet Interface” (Anbuky et al.) IEEE, Telecommunications Energy Conference (INTELEC 2000) there is disclosed a distributed system for gathering and storing state of charge information. Data analysis is distributed rather than centralised and there is no disclosure of a charging strategy to achieve state of charge equalisation.
WO 99/01918 discloses a battery management system in which individual cells may be selectively connected to a single cell battery charger or a variable load bank. However, connection to the single cell battery charger or variable load link is simply for determining the capacity of each battery rather than for performing any equalisation of the state of charge of batteries.
U.S. Pat. No. 5,701,068 discloses a battery management system in which each battery has an associated battery module for monitoring the battery and charging the battery. This is an expensive and complex system.
U.S. Pat. No. 6,043,628 discloses a battery management system in which a bypass arrangement is provided for each battery to reduce overcharging of selected batteries whilst allowing the remaining batteries to be charged. This requires an individual module with a bypass resistor arrangement for each cell and does not allow the selective charging of selected batteries.
U.S. Pat. No. 6,078,165 is a system for monitoring and charging only. No discharge capability is disclosed.
EP0798839A2 discloses a battery management system in which an individual battery module is required for each battery making it expensive and complex.
It is an object of the present invention to provide a battery management system that controls battery operation in a hybrid electric vehicle to optimise battery performance and extend the battery life.
It is a further object of the present invention to provide a battery management system for hybrid electric vehicles that overcomes, or at least ameliorates, the above mentioned problems with the prior art.
The above objections are to be read disjunctively with the object of at least providing the public with a useful alternative.